This is an interesting approach to the question of machine grading: "Clustering submissions along key metrics is a natural way to reduce the amount of work required. The hope is that homework submissions within the same cluster are similar enough, that feedback for one member can be propagated to the rest of the cluster... While this approach has yet to be used for grading, some instructors have used it to highlight common mistakes: clusters can also be used to identify common errors found in homework submissions."